On the margin of the lake where the feeder streams converge are a string of beaver ponds like tourmaline jewels. We paddle softly as we approach, portage neatly over the dam. We hardly notice its intricate web of mud and sticks, how with a minimum of materials it holds back the current and flattens it into a pool. We're not here to appreciate beavers (they're so secretive we rarely see them). We've come to the beaver ponds on this spring day to see ducks.